Dietary isoprenoids and isoprenoids and isoprenoids (nonsterols) derived from mevlonate, via the cholesterol biosynthesis pathway regulate 3- hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, a key enzyme of mevalonate biosynthesis. Mevalonate is required for the synthesis of isoprenoids such as ubiquinone, dolichol, isopentenyl tRNA, farnesyl and geranylgeranyl for the isoprenylation of proteins. A strong link exists between HMG-CoA reductase activity and tumor growth. Reductase inhibitors suppress tumor growth, by decreasing levels of farnesyl pyrophosphate, which is required for farnesylation of p21 (ras) and nuclear lamins, and subsequent DNA synthesis an cell division. Furthermore, reductase activity in tumor cells is elevated and resistant to sterol feedback regulation compared to normal cells. However, mevalonate biosynthesis in neoplastic cells is suppressed by nonsterol-mediated posttranscriptional control mechanisms that reduce tumor cell growth. Plant isoprenoids also decrease tumor growth via posttranscriptional suppression of reductase, either through increased enzyme degradation or decreased translational efficiency of its mRNA. Recently, we found that the plant-derived isoprenoid limonene, perillyl alcohol, and geraniol inhibit reductase synthesis in a manner analogous to that of mevalonate-derived nonsterols - via an unidentified translational control mechanism. Here we hypothesize that plant-derived isoprenoids and mevalonate modulate translational control of reductase synthesis through 5'-untranslated leader (UTL) or 3' untranslated (UT) sequences by decreasing either initiation of translation or the elongation rate on reductase mRNA, and that protein interactions with these sequences have a regulatory role. In aim number 1, reductase 5'-UTL and 3'-UT cDNA sequences will be ligated to a luciferase reporter gene, and isoprenoid effects on the translational efficiency of these fusion constructs evaluated tumor cells. In aim number 2, we will examine specific tumor-associated proteins interacting with untranslated sequences and define their role in translational control by first UV-cross linking proteins to mRNA and hybrid-selection of reductase-mRNPs, and secondly by gel-shift (RNA-protein binding) assays using reductase 5'-UTL and 3'UT transcripts. In aim number 3, we will examine the effects of limonene, perillyl alcohol and geraniol on leukemia cell growth and toxicity as well as Ras expression and synthesis. Our study will demonstrate at a molecular level how isoprenoids prevent uncontrolled cell growth, and provide insight into how plant-derived isoprenoids reduce the risk of developing cancer.